JPH07166020A - Methacrylic resin composition and its production - Google Patents

Abstract

PURPOSE:To obtain a composition inhibited from being thermally decomposed even when melt-kneaded at relatively high temperatures and therefore reduced in the generation of monomers by adding a specified amount of a specified organic disulfide compound to a methacrylic resin. CONSTITUTION:0.1-10ppm of an organic disulfide compound is added to a methacrylic resin comprising 50-100wt.% repeating units derived from methyl methacrylate and repeating units derived from another copolymerizable vinyl monomer. It is desirable that the organic disulfide compound is di-tert-dodecyl disulfide. This composition is obtained by melt-kneading a methacrylic resin with an organic disulfide compound in the substantial absence of oxygen, by previously adding an organic disulfide compound to the monomer and polymerizing the mixture into a methacrylic resin or by adding an organic disulfide to the mixture before withdrawing the resin after devolatilization in especially continuous bulk polymerization.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a methacrylic resin composition with reduced thermal decomposition in the melt-kneading step of a methacrylic resin, and a method for producing the methacrylic resin composition. Regarding Methacrylic resins obtained by polymerizing methyl methacrylate alone or together with other copolymerizable vinyl-based monomers have a transparency, surface gloss, weather resistance, chemical stability, etc. It is widely used because of its superiority. However, the methacrylic resin has a drawback that the molding conditions and the decomposition temperature of the methacrylic resin are close to each other, so that the methacrylic resin is poor in thermal stability at the time of molding and, eventually, the moldable temperature range is narrow. Therefore, it is necessary to take measures to prevent thermal decomposition of the methacrylic resin. Various methods have heretofore been proposed to prevent thermal decomposition of methacrylic resin. For example
In JP-A-57-9392 and JP-A-59-15444, thermal stability is improved by adding mercaptans.
When molded at a high temperature of ℃ or more, the thermal stability is not sufficient, and a strong mercaptan odor is produced. Also, JP-A-51-36258
As disclosed in Japanese Patent Publication No. 59-5215 and Japanese Patent Publication No. 59-5215, a method of adding 10 ppm to 1% of dialkyl disulfide, or a method of using dialkyl disulfide and phosphite triesters in combination is known. When used for, it has good thermal stability, but it has the drawbacks that it is colored during molding at high temperatures, and it produces a mercaptan odor during molding, which worsens the working environment. When used in combination, the coloring property is good, but the thermal stability is not sufficient and the transparency of the molded product is impaired. Further, a method of adding an amine compound, a metal soap or a hindered phenol compound has been proposed, but even if these stabilizers are used, there is almost no effect on thermal decomposition, transparency and There were problems such as deterioration of weather resistance. The present inventors have conducted diligent research to improve the thermal stability of methacrylic resin and reduce the amount of residual monomer resulting from thermal decomposition in the melt-kneading process. As a result, by adding a specific amount of a specific organic disulfide compound to the methacrylic resin, the unpleasant odor and coloring are extremely small without impairing transparency and weather resistance, and even when melt-kneading at a relatively high temperature, It was found that the increase in the amount of residual monomer of was reduced and was thermally stabilized, resulting in the present invention. That is, the present invention provides a methacrylic resin comprising 50 to 100% by weight of a methyl methacrylate unit and 50 to 0% by weight of another copolymerizable vinyl-based monomer unit, and an organic disulfide. 0.1-10 pp compound
A methacrylic resin composition characterized by being blended in an amount of less than m and a method for producing the same. The methacrylic resin used in the present invention may be not only a homopolymer of methyl methacrylate but also a copolymer of up to 50% by weight of the whole vinyl monomer copolymerizable therewith. Vinyl-based monomers copolymerized with methyl methacrylate include, for example, acrylic acid ester, methacrylic acid ester, acrylic acid, methacrylic acid, styrene,
It can be acrylonitrile or the like. Examples of the acrylate ester include methyl acrylate, ethyl acrylate and butyl acrylate, and examples of the methacrylate ester include ethyl methacrylate, butyl methacrylate and cyclohexyl methacrylate. Further, it may contain a diene rubber component, glutaric anhydride, or a glutarimide unit. The organic disulfide used in the present invention includes, for example, diethyl disulfide, di-n-propyl disulfide, di-sec-butyl disulfide and di-tert.
-Butyl disulfide, di-n-amyl disulfide,
Di-tert-amyl disulfide, di-tert-hexyl disulfide, di-n-octyl disulfide,
Di-tert-octyl disulfide, di-n-dodecyl disulfide, di-tert-dodecyl disulfide, di-n-stearin disulfide, ethyl-n-propyl disulfide, ethyl-tert-butyl disulfide, ethyl-sec-butyl disulfide, n -Dialkyl disulfides such as propyl-isopropyl disulfide; aromatic disulfides such as diphenyl disulfide, dibenzyl disulfide, di-p-tolyl disulfide; cyclic disulfides such as ditrimethylene disulfide, ditetramethylene disulfide, dicyclohexyl disulfide; cystine, Disulfides having an amino group such as diaminodiphenyl disulfide; dithiodiglycolic acid, dithiodipropionic acid, dithiodiglycolic acid-2- Disulfides of carboxylic acids and carboxylic acid derivatives such as ethylhexyl; a disulfide, and the like having an unsaturated bond such as diallyl disulfide.
Of these, di-tert-dodecyl disulfide is particularly preferable. In the present invention, the organic disulfide compound is 0.1 to 10 p based on 100 parts by weight of the methacrylic resin.
It is used in the range of less than pm, preferably 0.5 to 8.0 ppm. If the blending amount is less than 0.1 ppm, the effect of reducing the amount of residual monomer is not sufficient, the thermal stability is poor, and silver streak and coloring due to thermal burn are likely to occur when molding at high temperature. On the other hand, the compounding amount is 10 ppm
If it is above, when molded at a high temperature, the molded product is colored, and an unpleasant mercaptan odor is generated during molding, which causes deterioration of the working environment. In the present invention, if necessary, other additives such as other phenol-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, ultraviolet absorbers, hindered amine-based light stabilizers, lubricants, etc. , Pigments, dyes, flame retardants, foaming agents, reinforcing agents, inorganic fillers and the like may be added. In order to produce the methacrylic resin composition of the present invention, a monomer or syrup containing methyl methacrylate as a main component is mixed with the above organic disulfide compound in advance, and an ordinary methyl methacrylate is added as a main component. Known bulk polymerization for polymerizing a monomer or syrup, emulsion polymerization,
There are methods of polymerization such as suspension polymerization and solution polymerization. Among them, a method for producing a methacrylic resin by continuous bulk polymerization, that is, a syrup containing 40% to 70% of a polymer is obtained by bulk polymerization of a monomer containing methyl methacrylate as a main component. In the method of devolatilizing the volatile components such as monomers and taking out the resin, the organic disulfide compound is present before the devolatilization and taking out the resin. That is, there is a method in which the monomer is mixed with the organic disulfide compound in advance, or the resin is added before the resin is taken out in the subsequent steps, that is, at a place where it can be mixed with the resin. In addition, in order to produce the methacrylic resin composition of the present invention, a powdery material, a pelletized material, a pulverized material, etc. of the methacrylic resin and the organic disulfide compound are treated with Henschel in the substantial absence of oxygen. A method of using a mixer such as a mixer or a V-type blender, or mixing by means such as dry blending, and melt-kneading with a single-screw or twin-screw extruder;
Similarly, there is a method of melt-kneading simultaneously with melt processing such as injection molding and extrusion molding. When the organic disulfide compound is blended in the methacrylic resin production stage as in the former two cases, the composition obtained in the form of powder, pellets, lumps, etc., may be used as it is, or may be pulverized, or further optionally. The additive can be blended and used for molding such as injection molding and extrusion molding. When a methacrylic resin produced by a usual method like the third method is mixed with an organic disulfide compound, after mixing, a generally used single-screw or twin-screw extruder and various kneaders are used. Melt kneading with etc. to obtain an extruded product, or once pelletized with an extruder,
It can be a material for injection molding or extrusion molding. The present invention will be described in more detail with reference to the following examples, but these examples show preferred specific examples and do not limit the scope of the present invention. The percentages and parts in the examples are by weight unless otherwise stated. The evaluation methods used in the examples are as follows. Amount of residual monomer: 240 ° C. using an injection molding machine (M-140SJ type / manufactured by Meiki Seisakusho) having a capacity of 13 ounces,
A flat plate of 150 × 150 × 3 mm was molded at 260 ° C. and 270 ° C. A part of the obtained molded product was dissolved in methylene chloride and the residual monomer was measured by gas chromatography (GC-14A type / manufactured by Shimadzu Corporation). -Odor: In the above-mentioned injection molding, the presence or absence of odor near the mold immediately after the injection molding at 260 ° C was evaluated. -Coloring: In the above-mentioned injection molding, it was visually observed from the lateral direction (end face) of the injection-molded article when injection-molded at 260 ° C. Examples 1 to 3 Di-tert with respect to 100 parts of a monomer mixture consisting of 98% methyl methacrylate and 2% methyl acrylate.
-Dodecyl disulfide was added in the amounts shown in Table 1 and mixed. The monomer mixture thus prepared, 0.012 parts of azobisisobutyronitrile and 0.20 parts of octyl mercaptan were continuously supplied to a complete mixing type polymerization reactor, and the average residence time was 39 minutes, the temperature was 150 ° C, and the average temperature was 150 ° C. Polymerization was performed up to a polymerization rate of 45%. The obtained liquid polymer composition was heated to 200 ° C. and led to a devolatilizing extruder with a vent. At a devolatilizing extruder temperature of 250 ° C., unreacted monomer was taken out from the vent, the polymer was extruded in a molten state, water-cooled and then shredded into pellets, and the pellets were evaluated. The results obtained are shown in Table 1. Comparative Examples 1 to 3 Example 1 was repeated except that the addition amount of di-tert-dodecyl disulfide was changed as shown in Table 1.
The results obtained are shown in Table 1. Examples 4 to 6 100 parts of a copolymer consisting of 98% methyl methacrylate and 2% methyl acrylate and having a viscosity average degree of polymerization of 1100, and di-tert-dodecyl disulfide are shown in Table 1, respectively. Were dry-blended in an N ₂ stream, and then melt-kneaded at 250 ° C. by a vented extruder having a diameter of 40 mm and pelletized. The results obtained are shown in Table 1. Comparative Example 4 Example 4 was repeated except that the addition amount of di-tert-dodecyl disulfide was changed as shown in Table 1.
The results obtained are shown in Table 1. [Table 1] The methacrylic resin composition containing a specific organic disulfide compound according to the present invention suppresses thermal decomposition even when melt-kneaded at a high temperature and generates less monomer. Therefore, this composition can extend the molding processing temperature range of the methacrylic resin and improve the production stability.

Claims (1)

Claim: What is claimed is: 1. A methacrylic resin comprising 50 to 100% by weight of a methyl methacrylate unit and 50 to 0% by weight of another copolymerizable vinyl monomer unit, and an organic disulfide compound in an amount of 0.1 to 0.1% by weight. A methacrylic resin composition comprising less than 10 ppm. 2. An organic disulfide compound is di-tert-
The methacrylic resin composition according to claim 1, which is dodecyl disulfide. 3. A methacrylic resin consisting of 50 to 100% by weight of a methyl methacrylate unit and 50 to 0% by weight of another copolymerizable vinyl-based monomer unit, and substantially 0.1 to less than 10 ppm of an organic disulfide compound. The method for producing a methacrylic resin composition according to claim 1, which comprises melt-kneading in the absence of oxygen. 4. The method for producing a methacrylic resin composition according to claim 1, wherein a monomer is previously made to contain the organic disulfide compound and the resulting compound is polymerized to produce a methacrylic resin. 5. The method for producing a methacrylic resin composition according to claim 1, wherein when the methacrylic resin is produced by continuous bulk polymerization, the organic disulfide compound is present before the resin is taken out through the devolatilization step.